As shown in FIG. 7, a conventional unidirectional ratchet wrench contains a driving head 40, the driving head 40 has a driving member 41 and a toothed portion 42 for retaining with a retaining block 44 of a groove 43, and the groove 43 has a hole 47 defined therein and having a returning spring 46 fixed in the hole 47. One end of the returning spring 46 abuts against a connecting extension 45 of the retaining block 44, such that the returning spring 46 presses the retaining block 44 to move inwardly so as to form a space, such that when an operational direction of the unidirectional ratchet wrench is identical to an arrangement direction of the retaining block 44, the retaining member 44 rotates a workpiece in a single direction.
However, the returning spring 46 is fatigued after a long period of using time, so it disengages from the hole 47 or from the connecting extension 45, In addition, the hole 47 has to be drilled, thus increasing production cost.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.